Mountain ranges, rising to over 1500m, divide Sarawak from Kalimantan. Heavy tropical rainfall in the mountains produces many streams which combine as they descend through rough broken hill country to form mighty rivers including the Rajang and Sadong. The highest point in Sarawak is Mt.Murud at 2424m, from which flow the Baram, Limbang and Trusan rivers. Most of the accessible hills have been cleared of forest for agriculture. The foothills give way to swamps, which predominate in low-lying areas. In the south-west the mountains are nearer the coast. Transport in the past was wholly by river, but now a sealed highway traverses the state.

VEGETATION

The forest vegetation of Sarawak may be divided into nine types:

• beach forest,
• mangrove forest,
• brackish swamp,
• peat swamp forest,
• heath forest,
• forest over limestone,
• tropical lowland evergreen rainforest,
• tropical lower montane forest, and tropical upper montane forest.

Beach forest comprises mainly herbaceous plants, Casuarina equisetifolia, coconuts and other waterborne tree seeds. Mangrove forest or mangals consists of over 50 species adapted to a saline environment. Mangroves are harvested for firewood, cutch for tanning, poles for piling and scaffolding, hopefully on a cycle of not less than 25 years. Brackish swamp comprises almost exclusively Nypa Nypa fruticans, with sometimes a belt of Nibong Oncosperma filamentosa on the landward side. Peat swamp forest occupies nearly the entire coastline and covers 15,000 square kilometres. It produced much of Sarawak's commercial timber, but is now almost totally depleted of timber trees. It was dominated by trees such as Alan Shorea albida up to 60m tall and also included Jongkong Dactylocladus stenostachys, Ramin Gonystylus bancanus, Sepetir Copaifera palustris, Kapur Dryobalanops rappa and Meranti Shorea spp. Heath forest occurs on the coast and inland and is dominated by trees of small trunk diameter. Pole forest is known to the Ibans as kerangas, land carrying forest, which when cleared will not grow hill rice. A wet heath forest occurs on some badly drained areas of podzolic soils and is known as kerepah by the Ibans. Forest over limestone has a diverse flora including Casuarina nobilis. There are few dipterocarps, and Boea spp. cling to the vertical walls.

Beach Vegetation - Pasir Puteh Mangroves - Similajau National Park Montane Forest

Tropical lowland evergreen rainforest, or mixed dipterocarp forest, MDF, extends from sea level to 750m. Most has been cleared for agriculture or has been logged except in inaccessible areas. Secondary forest develops after logging, where agriculture is not practised. Lowland dipterocarp forest extends up to 300m, consisting of numerous dipterocarps, especially Keruing Dipterocarpus spp., Meranti and Selangan Batu Shorea spp., Drybalanops aromatica, and Bornean Ironwood or Belian Eusideroxylon zwageri. Tropical conifers Sempilor Dacrydium elatum, and Bindang Agathis alba are uncommon. There are numerous epiphytes, climbers and stranglers. Hill dipterocarp forest extends from 300m to 750m and includes the previously listed species with Shorea curtisii.

Tropical lower montane rainforest extends from 750m to 1500m. From 750m to 1200m it is upper dipterocarp forest, including Shorea platyclados, S.ciliata, S.ovata and Dipterocarpus retusus. Lower montane forest differs from lowland rainforest in having a lower canopy averaging 25m as opposed to 35m, with few emergents. There is a decrease in biomass and leaf size with increasing altitude. Buttresses are few and epiphytes abundant. Fagaceae spp. and Lauraceae spp. appear, becoming more common ascending to the upper montane forest.

In Sarawak, upper montane forest extends from 1500m to the mountain summits. The canopy is lower than lower montane forest dropping to 10m or less, where heath forest occurs and Leptospermum sp. prevails. Moss forest occurs where cloud cover is regular. Species of conifers, Myrtaceae, Rhododendron and Vaccinium are common at this elevation.

Tropical upper montane forest.
Beach forest comprises mainly herbaceous plants, Casuarina equisetifolia, coconuts and other waterborne tree seeds.

Mangrove forest or mangals consists of over 50 species adapted to a saline environment. Mangroves are harvested for firewood, cutch for tanning, poles for piling and scaffolding, hopefully on a cycle of not less than 25 years.

Brackish swamp comprises almost exclusively Nypa Nypa fruticans, with sometimes a belt of Nibong Oncosperma filamentosa on the landward side.

Peat swamp forest occupies nearly the entire coastline and covers 15,000 square kilometres. It produced much of Sarawak's commercial timber, but is now almost totally depleted of timber trees. It was dominated by trees such as Alan Shorea albida up to 60m tall and also included Jongkong Dactylocladus stenostachys, Ramin Gonystylus bancanus, Sepetir Copaifera palustris, Kapur Dryobalanops rappa and Meranti Shorea spp.

Heath forest occurs on the coast and inland and is dominated by trees of small trunk diameter. Pole forest is known to the Ibans as kerangas, land carrying forest, which when cleared will not grow hill rice. A wet heath forest occurs on some badly drained areas of podzolic soils and is known as kerepah by the Ibans.

Forest over limestone has a diverse flora including Casuarina nobilis. There are few dipterocarps,and Boea spp. cling to the vertical walls.

Tropical lowland evergreen rainforest, or mixed dipterocarp forest, MDF, extends from sea level to 750m. Most has been cleared for agriculture or has been logged except in inaccessible areas. Secondary forest develops after logging, where agriculture is not practised. Lowland dipterocarp forest extends up to 300m, consisting of numerous dipterocarps, especially Keruing Dipterocarpus spp., Meranti and Selangan Batu Shorea spp., Drybalanops aromatica, and Bornean Ironwood or Belian Eusideroxylon zwageri. Tropical conifers Sempilor Dacrydium elatum, and Bindang Agathis alba are uncommon. There are numerous epiphytes, climbers and stranglers. Hill dipterocarp forest extends from 300m to 750m and includes the previously listed species with Shorea curtisii.

Tropical lower montane rainforest extends from 750m to 1500m. From 750m to 1200m it is upper dipterocarp forest, including Shorea platyclados, S.ciliata, S.ovata and Dipterocarpus retusus. Lower montane forest differs from lowland rainforest in having a lower canopy averaging 25m as opposed to 35m, with few emergents. There is a decrease in biomass and leaf size with increasing altitude. Buttresses are few and epiphytes abundant. Fagaceae spp. and Lauraceae spp. appear, becoming more common ascending to the upper montane forest.

In Sarawak, upper montane forest extends from 1500m to the mountain summits. The canopy is lower than lower montane forest dropping to 10m or less, where heath forest occurs and Leptospermum sp. prevails. Moss forest occurs where cloud cover is regular. Species of conifers, Myrtaceae, Rhododendron and Vaccinium are common at this elevation.